pl.when(...).otherwise(...) fails for predicate involving struct fields

[nsfinkelstein]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

import polars as pl
df = pl.DataFrame({'json': [{'a': 1}, {'a': None}]})
condition = pl.all_horizontal(pl.col('json').struct.field(f).is_null() for f in df['json'].struct.fields)
fixed_df = df.with_columns(pl.when(condition).then(None).otherwise(pl.col('json')))

Log output

shape: (2, 2)
┌───────────┬───────────┐
│ json      ┆ literal   │
│ ---       ┆ ---       │
│ struct[1] ┆ struct[1] │
╞═══════════╪═══════════╡
│ {1}       ┆ null      │
│ {null}    ┆ {null}    │
└───────────┴───────────┘

Issue description

The correct behavior can be triggered by switching out otherwise for a then with an explicit negation of the condition, which should be equivalent but is not.

import polars as pl
df = pl.DataFrame({'json': [{'a': 1}, {'a': None}]})
condition = pl.all_horizontal(pl.col('json').struct.field(f).is_null() for f in df['json'].struct.fields)
fixed_df = df.with_columns(pl.when(condition).then(None).when(~condition).then(pl.col('json')))

This yields the correct output.

shape: (2, 2)
┌───────────┬───────────┐
│ json      ┆ literal   │
│ ---       ┆ ---       │
│ struct[1] ┆ struct[1] │
╞═══════════╪═══════════╡
│ {1}       ┆ {1}       │
│ {null}    ┆ null      │
└───────────┴───────────┘

Expected behavior

The output dataframe is the correct dataframe shown above.

Installed versions

--------Version info---------
Polars:              1.9.0
Index type:          UInt32
Platform:            Linux-5.10.219-208.866.amzn2.x86_64-x86_64-with-glibc2.35
Python:              3.11.9 (main, Sep 23 2024, 17:32:51) [GCC 11.4.0]

----Optional dependencies----
adbc_driver_manager  <not installed>
altair               <not installed>
cloudpickle          3.0.0
connectorx           <not installed>
deltalake            <not installed>
fastexcel            <not installed>
fsspec               2024.9.0
gevent               <not installed>
great_tables         0.13.0
matplotlib           3.9.2
nest_asyncio         1.6.0
numpy                1.26.4
openpyxl             <not installed>
pandas               2.2.3
pyarrow              17.0.0
pydantic             2.9.2
pyiceberg            <not installed>
sqlalchemy           2.0.35
torch                2.3.1+cu121
xlsx2csv             <not installed>
xlsxwriter           <not installed>

[cmdlineluser]

I believe this is fixed on main. #19148

>>> fixed_df
shape: (2, 2)
┌───────────┬───────────┐
│ json      ┆ literal   │
│ ---       ┆ ---       │
│ struct[1] ┆ struct[1] │
╞═══════════╪═══════════╡
│ {1}       ┆ {1}       │
│ {null}    ┆ null      │
└───────────┴───────────┘

[ritchie46]

I will close as this is fixed on main. Will release this weekend.